The invention relates to the field of automatic bursting of perforated continuous forms. More particularly, the invention relates to an improvement of an apparatus for bursting forms which includes means for achieving forms uncrinkling through allowing forms slippage and means for accomplishing forms separation in the event of forms slippage.
In well known prior art bursting apparatus, a pair of high speed rollers and a pair of low speed rollers coact with a bursting blade to achieve separation along the preweakened zones of continuous paper forms. In such devices the continuous forms would be drawn between the upper and lower low speed rollers as they rotated. The forms could then be propelled beneath the burster bar and thence to the rotating upper and lower high speed rollers. At this point the speed differential between the high speed and low speed rollers would cause the forms to be tightly stretched. The placement of the bursting bar would be set to cause the preweakened zone of the continuous forms to arrive at a point directly beneath the bursting area of the bursting bar at the moment of maximum forms stretch. The perforation of the forms would be pushed tauntly against the bursting area of the bursting bar, thus initiating a line of separation along the perforations of the continuous forms. When separation would be completed, the high speed rollers would cause the separated form to be ejected toward a stacking means. The continuous forms would then be propelled to the upper and lower high speed rollers for bursting along the next line of perforation.
An improvement disclosed in U.S. Pat. No. 4,118,022 is to provide two pairs of flat areas formed into the bearing surface of the upper roller of the low speed roller pair which first receives the forms. The flat areas improve the reliability of the forms feeding process by enabling removal of crinkles which frequently occur in the forms as they pass through the rollers. When a flat area on the upper roller faces the lower roller, the nip for gripping and feeding the forms defined by the mating upper and lower rollers is released, allowing the forms to slip and remove crinkles. In practice, however, it has been found that a disadvantage of having such flat areas is that when the forms slip, the preweakened zones slip past the burster bar such that the perforated zone is no longer at the right position with respect to the bursting bar for separation to occur. This results in jamming of the bursting apparatus and the necessity of stopping the system and unjamming it by hand.